Method of recovering drill pipe from wells



Sept. 22, 1959 A. BELL EI'AL METHOD OF RECOVERING DRILL PIPE FROM WELLSFiled Jan. 19, 1953 Aw Au v m v X 1N VENTORS United States PatentNIETHOD OF RECOVERING DRILL PIPE FROM WELLS Leo A. Bell and Edwin H.Helm, Odessa, Tex., assignors to The Dia-Log Tubular Survey Company, LosAngeles, Calif., a copartuership Application January 19, 1953, SerialNo. 331,963

6 Claims. (Cl. 2551.8)

This invention relates to a method and apparatus of recovering a stuckdrill pipe from wells.

Explanatory of the present invention, practically all well holes drilledby a rotary well drilling apparatus depart more or less from the truevertical. The amount of departure from the true vertical is to a largeextent dependent upon the type of formation that is being drilledthrough. Other influential factors are the weight placed on the bit, thespeed of rotation, and the volume of circulation. By way ofillustration, a well hole drilled by the rotary well drilling apparatusmay depart from the vertical from /2 to 2 to the north for five hundredfeet of depth, then reverse the direction of its departure from thevertical and be /2" to 2 off toward the south or some other directionfor the next five hundred feet or one thousand feet of depth. It is notuncommon for a well hole in plan to wander around through a completecircle and for it in vertical section to reverse the direction of itsdeparture from the vertical several times. Wherever the hole does departfrom the vertical there is produced a location of a possible key seatinasmuch as when the drill pipe is run into or out of the hole or whileit is being rotated in tension opposite the inside of the bend in thehole it tends to cut or wear a hole in the well wall at the inside ofthe bend. If, for example, the well is being drilled with a 12%" bitusing 4 /2" drill pipe with 6%" OD. tool joints, the drill pipe willtend to cut a 6% hole in the well wall on the inside of the bend in thedrilled hole. If the drill string is equipped with 7" or 8" drillcollars above the bit these drill collars cannot pass through the 6%"hole or key seat formed in the well walls. Consequently, if the drillpipe is being pulled rapidly from the well to replace the bit or forother purposes, the drill collars may start to enter the key seat ratherthan follow the curvature of the 12%" hole. The high speed at which thedrill string is being elevated and the momentum of the drill stringfrequently causes the drill collars to enter the key seat and becomeimmovably lodged therein.

The key seats above referred to frequently occur where the strata of theformation being drilled is of varying hardness and solubility. In thePermian Basin of West Texas and New Mexico there is what is commonlyreferred to as the salt section. This salt section in some areas is asmuch as two thousand feet in thickness and within it at random depthsare stringers of anhydrite which vary in thickness from 1 to Whiledrilling through the salt section the water of the drilling fluid tendsto dissolve and wash out the salt leaving the harder stringers ofanhydrite as ledges. The washed out or dissolved out sections of saltoften create cavities of great size immediately beneath the hard ledgesof anhydrite and there have been many experiences where fish left in thewell have leaned or fallen back into these cavities to such an extentthat they cannot be located or engaged by a fishing tool. Similarconditions conducive of the formation of key seats are also found inmany sedimentary basins where there are stringers or ice hard stratacommonly referred to as shells. These might, for example consist of arelatively hard cemented sandstone overlying softer bodies of shalewhich are susceptible of being washed out by the circulation fluid toform large cavities in the well walls beneath the shells. The ledges ofanhydrite and the shell stringers tend to stand out around the drilledhole as hard ledges and the action of the drill pipe on the inside of abend in the hole cuts a reduced size hole into them. This produces anideal situation for the drill collars to become stuck when the drillpipe is being rapidly withdrawn from the hole.

Heretofore, under the circumstances above referred to, customaryprocedures for endeavoring to free the drill string and recover it fromthe hole have been to first attempt to locate the depth of the key seator the .stuck point along the length of the drill string. This can bedone by lowering into the drill pipe any one of a number of free pointindicators now available on the market. These free point indicators arein the nature of electrical strain gauges that can be seated in the pipeat various elevations. Stresses, either torsional or axial, are thenimposed on the pipe and the strain of that portion of the pipe oppositethe strain gauge is determined from the strain gauge. By locating thestrain gauge at various depths and noting whether or not it is actuatedby imposing a strain on the pipe the approximate point at which thedrill string is stuck in the well can be ascertained. It has also beencommon practice to impose a tension on the drill pipe at the surface,note the amount of elongation produced in the pipe by the tensionimposed and from this information compute or estimate the length ofdrill pipe down from the surface that is free. This latter practicewhich is now rapidly becoming obsolete, afiords another method by whichthe stuck point in the drill pipe can be approximately located. Afterthe stuck point has been located, the operator then usually backs off orunscrews the drill pipe some distance above the stuck point. This isfrequently accomplished by imposing an unscrewing torque on the drillpipe and exploding a small explosive charge within the tool joint thatit is desired to unscrew. Sometimes inside cuts are made in the drillpipe rather than attempting to unscrew at a tool joint. When the drillpipe is thus separated the upper portion of the drilling string isrecovered from the hole, leaving the lower portion or fish therein.Generally, the operator will then follow one of three general programsin attempting to recover the fish that has become immovably lodged inthe key seat.

One such program consists of again connecting to the fish either byscrewing into it or by the use of an overshot and using jars, a bumpersub, and several heavy drill collars and attempting to bump the fishdown out of the key seat or to jar it up the hole and out of the keyseat.

A second procedure is to run in with a wash pipe and wash over the fish,thus removing the key seat and permitting the fish to fall to the bottomof the well and then attempting to recover the fish from the bottom.

The third procedure is to wash over the fish and attempt to catch thefish with a dog overshot, preventing it from falling to the bottom ofthe well. Regardless of which procedure is followed there aredisadvantages, and recovering of the fish may either be very difficultor in some cases impossible. That is, since the drill string has beenbacked off or cut off two or three joints above the stuck point in orderto have a portion which may be engaged protruding from the top of thekey seat, there is thus an upstanding length of free drill pipe standingabove the key seat. This upstanding portion is comparatively limber andobviously does not provide a good means of transmitting the blow from abumper sub or jars down to the stuck point. If the washover procedure isfollowed and the fish is permitted to fall to the bottom of the well,the operator is always faced with the problem of having the fish stick asecond time in the well, and there is danger of the upper end of thefish falling or leaning back into a cavity beneath the anhydrite ledgeor shell ledge, making it extremely diflicult to engage and recover thefish.

A primary object of the present invention is to provide an improvedmethod for recovering a drill string which has become immovably lodgedin a key seat in a well wherein, instead of detaching the upper portionof the drill string from that portion which has become immovably lodgedin the key seat, the drill string is left intact. Consequently, there isno danger of the fish dropping to the bottom of the hole when loosenedand no danger of the fish falling or leaning back into a cavity in thewell walls and the difficulties involved in re-engaging the fish areentirely eliminated.

More specifically, an object of the present invention is to provide animproved method of recovering drill strings that have become immovablylodged in key seats where in the stuck point along the length of thestring is located or approximated and an explosive is exploded in thewell on the exterior of the drill string in the neighborhood of thestuck point. The explosive is preferably set off while the drill stringis stressed in a direction tending to dislodge it from the key seat.When the explosive is exploded the key seat, either may be destroyed orat least the drill string is loosened therefrom so that it canthereafter be recovered from the well without having been previouslyseparated.

With the foregoing and other objects in view, which will be mademanifest in the following detailed description and specifically pointedout in the appended claims, reference is had to the accompanyingdrawings for an illustrative embodiment of the invention, wherein:

Figure 1 is a vertical section through a portion of a Well illustratingin a somewhat exaggerated manner, a drill string immovably lodged in akey seat, and illustrating apparatus employed for freeing the drillstring; and

Fig. 2 is a horizontal section taken substantially upon the line 22 uponFig. l in the direction indicated.

Referring to the accompanying drawings wherein similar referencecharacters designate similar parts throughout, indicates a well borewhich may be regarded as having been drilled by means of a bit 11 abovewhich there may be one or more drill collars 12 by which the bit isattached to a string of drill pipe 13, the sections of which areconnected to each other by means of tool joints 14. As has beenindicated in a rather exaggerated manner, the well bore 10 has deviatedfrom the vertical and is shown as having subsequently returned to thevertical so that the bore has a bend therein generally indicated at 15.On the inside of this bend, as drilling has progressed, the tool joints14 have worn or cut a recess in the well wall, indicated at 16, formingWhat has commonly been referred to in the field as a key seat. Asillustrated in the drawing, this key seat has a size substantially equalto the outside diameter of the tool joints. In withdrawing the drillpipe from the well to replace the bit 11, or for other purposes, thedrill collars 12, which usually are of greater diameter than the tooljoints 14, are illustrated as having been forced into the bottom of thekey seat so as to become immovably lodged therein. This usually occurswhen the drill pipe is being elevated in the well at a rapid rate. Asimilar situation may be created when the drill string is being lowered.Under the latter circumstance the bit or a portion of it, and sometimesportions of the drill collars, enter into the top of the key seat andbecome immovably lodged therein.

In order to free the drill pipe the stuck point along the length of thedrill string is first ascertained. This may be accomplished by loweringa free point indicator through the drill pipe 13. Any one of a number(iiiferent designs of free point indicators may be used for thispurpose. In the illustration on the drawing such free point indicatorwould probably indicate that the drill pipe 13 is free above the drillcollars 12 but that the top of the drill collars is the point at whichthe drill string has become stuck in the key seat. It is possible,however, that for one reason or another a tool joint has become stuck inthe key seat, in which case the free point indicator would indicate thisfact or that point along the length of the drill string that is stuck.

After having ascertained the point or depth along the length of thedrill string at which it is stuck in the casing a cable 17 containing anelectric conductor is lowered into the well bore 10 on the exterior ofthe drill string. This cable is connected to a rope socket 18 to whichthere is connected a shootingadapter 19. The conductor in the cableindicated at 20 is connected to a detonating cap 21 beneath which thereis disposed an adequate length of explosive, indicated at 22. Thisexplosive may be any one of a number of different types of explosives. Atypical explosive consists of plastic-covered Primacord having grainsper foot. The average size of the explosive consists of twenty stringsof 100 grain Primacord, fifty feet long, although the amount ofexplosive employed may be increased or decreased to meet variousconditions. The strings of Primacord are arranged in side by siderelationship beneath the detonating cap and are bound by means of tiesor the equivalent indicated at 23 to a socalled by-pass line indicatedat 24. This by-pass line consists of a cable preferably formed of colddrawn plow steel having a high tensile strength such that it will not beapt to be blown in two when subjected to the explosion of the explosive.The by-pass line has its upper end connected to the shooting adapter 19and has a weight 25 wired as at 26 to the bottom of the by-pass line.The weight 25 is preferably in the form of a thin-walled metal containerfilled with lead shot. The wire tie at 26 is such that, after theexplosive has been exploded in the event that the weight 25 becomescaught in the well in the course of Withdrawing the cable 17 the wiretie will part before pulling out pull-out blocks conventionally employedin the rope socket 18. In this manner the weight can be released and dueto its thin wall and the nature .of its contents the weight maysubsequently readily be drilled up. In lieu of using the by-pass line 24the weight 25 may be connected directly to the explosive 22 which, ofcourse, would involve a release of the weight when the explosive isexploded. The by-pass line enables recovery of the weight from the wellin the event that the weight is not caught in the well in the course ofits withdrawal.

The explosive 22 which is lowered into the well bore 10 on the outsideof the drill string is positioned so as to extend from a point below thestuck point as determined by the free point indicator to a point somedistance above the stuck point. When the explosive has been thuspositioned a stress is applied to the drill string tending to dislodgeit. Thus if the drill string has become immovably lodged in the key seatin the course of withdrawal of the drill string, the weight of the drillstring would be imposed in a downward direction. Conversely, if thedrill string has become lodged in the key seat in the course of loweringthe drill string into the well, an upward tension would be imposed onthe drill string tending to free it from the key seat. While stress isthus imposed on the drill string the explosive 22 is exploded along thekey seat and above and below the stuck point as determined by the freepoint indicator. Exactly what takes place in the well cannot beaccurately ascertained. At all events when the explosive is thusexploded it is usually found that the drill string is immediately freedand may be recovered from the well. This may result from a completedestruction of the key seat or the well walls around the key seat, or itmay be due to a combination of the stress imposed on the drill stringcoupled with the sudden jar created by the explosion. After theexplosive has been exploded the line 17 is withdrawn from the well andthe drill pipe recovered.

As above explained, the well bore may wander in several diiferentdirections so that when the drill string is suspended therein the drillpipe may be in close proximity to one side of the well bore at one depthand in close proximity to another side of the well bore at anotherdepth. In the course of lowering the explosive into the well the weight25 will descend between the drill pipe and a side of the well bore towhich it is closely adjacent. Consequently it is frequently desirable towork the pipe in the well during the course of lowering the explosive.This consists of alternately imposing tension on the drill pipe so as tostretch it, and releasing it. This working of the pipe will usuallyfacilitate the passage of the explosive down through the well bore onthe exterior of the pipe.

It may happen that as the explosive is being lowered into the welladjacent the drilling string that it may progress around the drillingstring so that the lowering cable or line is given a complete wraparound the drilling string. Under such circumstances further lowering orwithdrawal of the line is prevented. This may be overcome by lowering aback-oft shot down the inside of the pipe and exploding it so that thepipe may be unscrewed and rotated. The back-otf shot referred to hereinis the conventional back-01f shot consisting of an elongated explosivewhich is lowered into the drill string and which .is incapable ofdestroying the drill string. It is set off usually on the interior of atool joint while the drill string is stressed in torque, tending tounscrew the tool joint. The shock of the explosive causes the tool jointto loosen and unscrew under this reverse torque. When the tool joint hasbeen thus loosened, it enables that portion of the drill string abovethe loosened tool joint to be rotated. Rotation of the pipe will tend tounwind the line from the exterior thereof and thus enable its beingfurther lowered or its being recovered. Thereafter, the separateddrilling string may be reconnected and recovered.

From the above described method and apparatus it will be appreciatedthat in the usual situation it is not necessary to detach the upperportion of the drill string from the lower portion or stuck portionthereof. Consequently there is no occasion to drop the lower portion orfish in the well with the resulting danger of the fish falling orleaning into a cavity in the well wall below the key seat. The methodabove described has heretofore proven very successful in recoveringdrilling strings from wells where the drill string has become immovablylodged in a key seat.

Various changes may be made in the details of the construction withoutdeparting from the spirit and scope of the invention as defined by theappended claims.

We claim:

1. The method of recovering a drill string which has become immovablylodged in a key seat in a well which comprises ascertaining theapproximate point along the length of the drill string at which it isstuck, lowering an explosive into the well on the exterior of the stringto the neighborhood of the stuck point which explosive is incapable ofdestroying and parting the drill string, setting ofi the explosive atthe mentioned neighborhood of the stuck point while that portion of thedrill string adjacent the stuck point is under stress tending todislodge it from the key seat, and withdrawing the drill string from thewell.

2. The method of recovering a drill string which has become immovablylodged in a key seat in a well which comprises ascertaining theapproximate point along the length of the drill string at which it isstuck, lowering an explosive on a line into the well on the exterior ofthe string to the neighborhood of the stuck point which ext plosive isincapable of destroying and parting the string, imposing a stress on thedrill string tending to dislodge it from the key sea-t, exploding theexplosive in the well on the exterior of the drill string in theneighborhood of the stuck point, and withdrawing the drill string fromthe well.

3. The method of recovering a drill string which has become immovablylodged in a key seat in a well which comprises ascertaining theapproximate point along the length of the drill string at which it isstuck, lowering an elongated explosive into the well on the exterior ofthe string to the neighborhood of the stuck point which explosive isincapable of destroying and parting the string, exploding the explosivein the well on the exterior of the drill string in the neighborhood ofthe key seat while that portion of the drill string adjacent the stuckpoint is under axial stress tending to dislodge it from the key seat,and withdrawing the drill string from the well.

4. The method of recovering a drill string which has become immovablylodged in a key seat in a well which comprises ascertaining theapproximate point along the length of the drill string at which it isstuck, lowering an explosive into the well on the exterior of the stringwhich explosive is incapable of destroying and parting the string,working the drill string while lowering the explosive, exploding theexplosive in the well on the exterior of the drill string in theneighborhood of the stuck point, and withdrawing the drill string fromthe well.

5. The method of recovering a drill string which has become immovablylodged in a key seat in a well which comprises ascertaining theapproximate point along the length of the drill string at which it isstuck, lowering an explosive into the well on the exterior of the stringto the neighborhood of the stuck point which explosive is incapable ofdestroying and parting the string, lowering a back-oil shot in the drillstring, reverse torquing the drill string, setting ofi the back-off shotand unscrewing and rotating the thus loosened portion of the drillstring to unwrap the line used to lower the explosive in the well in theevent that such line has become wrapped around the drill string,exploding the explosive in the well on the exterior of the string in theneighborhood of the stuck point, and withdrawing the drill string fromthe well.

6. The method of recovering a drill string which has become immovablylodged in a key seat in a well which comprises ascertaining theapproximate point along the length of the drill string at which it isstuck, lowering an explosive into the well on the exterior of the stringto the neighborhood of the stuck point which explosive is incapable ofdestroying and parting the string, lowering a back-ofi shot in the drillstring, reverse torquing the drill string, setting oif the back-01f shotand unscrewing and rotating the thus loosened portion of the drillstring References Cited in the file of this patent UNITED STATES PATENTS2,259,564 Holland Oct. 21, 1941 2,304,793 Bodine Dec. 15, '1942.2,305,261 Kinley Dec. 15, 1942 2,414,349 Alexander Jan. 14,19472,650,539 Greene Sept. 1, 1953 OTHER REFERENCES The Oil and Gas Journal,vol. 38, No. 47, Apr. 4, 1940, pages 39, 40, 43, 44 and 57.

